1. Field of the Invention
The present invention relates generally to an improved method for reducing distal embolization during treatment of emboli, thrombi and other types of occlusions in the human arterial or venous system. The method is particularly well suited for use when treating stenoses or occlusions within saphenous vein grafts, coronary arteries, cerebral arteries and similar vessels.
2. Description of the Related Art
Human blood vessels often become occluded or completely blocked by plaque, thrombi, emboli or other substances, which reduces the blood carrying capacity of the vessel. Should the blockage occur at a critical location in the circulation, serious and permanent injury, or death, can occur. To prevent this, some form of medical intervention is usually performed when significant occlusion is detected, such as during an acute myocardial infarction (AMI).
Coronary heart disease is the leading cause of death in the United States and a common occurrence worldwide. Damage to or malfunction of the heart is caused by narrowing or blockage of the coronary arteries (atherosclerosis) that supply blood to the heart. The coronary arteries are first narrowed and may eventually be completely blocked by plaque, and may further be complicated by the formation of thrombi (blood clots) on the roughened surfaces of the plaques. AMI can result from atherosclerosis, especially from an occlusive or near occlusive thrombus overlying or adjacent to the atherosclerotic plaque, leading to death of portions of the heart muscle. Thrombi and emboli also often result from myocardial infarction, and these clots can block the coronary arteries, or can migrate further downstream, causing additional complications.
Various types of intervention techniques have been developed which facilitate the reduction or removal of the blockage in the blood vessel, allowing increased blood flow through the vessel. One technique for treating stenosis or occlusion of a blood vessel is balloon angioplasty. A balloon catheter is inserted into the narrowed or blocked area, and the balloon is inflated to expand the constricted area. In many cases, near normal blood flow is restored. It can be difficult, however, to treat plaque deposits and thrombi in the coronary arteries, because the coronary arteries are small, which makes accessing them with commonly used catheters difficult.
Other types of intervention include atherectomy, deployment of stents, introduction of specific medication by infusion, and bypass surgery. Each of these methods is not without the risk of embolism caused by the dislodgment of the blocking material which then moves downstream. In addition, the size of the blocked vessel may limit percutaneous access to the vessel.
There is a need for an improved method of reducing distal embolization during treatment of occluded vessels that can be performed regardless of the size of the blood vessel.
Described below is an improved method for preventing distal embolization during removal of plaque, thrombi or other occlusions from a blood vessel. In a preferred embodiment of the invention, aspiration is performed while advancing a guidewire across the site of the occlusion in a proximal to distal direction to prevent distal embolization. An aspiration catheter is delivered over the guidewire until the distal ends of the guidewire and aspiration catheter are just proximal to the site of the occlusion. While aspirating, the occlusion in the vessel is crossed with both the guidewire and the catheter in a proximal to distal direction. In a preferred embodiment, the distal tip of the aspiration catheter is no more than 2 cm, more preferably no more than 0.5-1 cm, behind or proximal to the distal tip of the guidewire during crossing. The distal end of the aspiration catheter is then moved back across the occlusion, while continuously aspirating, to ensure the removal of any particles which may be created during the delivery of the guidewire to a position distal to at least a portion of the occlusion. Aspiration from proximal to distal, and distal to proximal, can be repeated as many times as necessary to completely aspirate all particles. These steps are all performed prior to any occlusion of the vessel using an occlusive device at a site distal to the occlusion, and treatment of the occlusion, as described below.
In another preferred embodiment of the invention, a guidewire having an occlusive device on its distal end is advanced across the occlusion such that the occlusive device is distal to the occlusion, where it is then actuated. An aspiration catheter is delivered over the guidewire to a location proximal to the occlusion. Delivery of the aspiration catheter can occur before or after actuation of the occlusive device. While the occlusive device is actuated, the distal end of the aspiration catheter is moved in a proximal to distal direction across at least a portion of the occlusion while aspirating at the same time. Alternatively, aspiration may begin after the distal end of the aspiration catheter is moved distal to at least a portion of the occlusion, and the aspiration catheter may be moved in a distal to proximal direction. Furthermore, regardless of whether aspiration begins proximal or distal to the occlusion, aspiration may continue in both proximal to distal and distal to proximal directions and repeated as necessary to completely aspirate particles.
The aspiration method disclosed herein can be used in any vessel of the body where the pressure is at least 0.2 psi at any time during the diastolic/systolic cycle of the heart, and, preferably, is about 1.2 psi, and is capable of providing a flow rate of at least 5 cc/minute when not occluded. Thus, although the pressure within any vessel may fall below 0.2 psi during relaxation between heartbeats, so long as the pressure created by the heartbeat rises to at least 0.2 psi, the pressure within the vessel will be sufficient.
The present method is particularly suited for use following myocardial infarction, and in removal of occlusions from saphenous vein grafts, coronary and carotid arteries, and vessels having similar pressures and flow.
In a preferred embodiment of the method of the present invention, a guide catheter is first introduced into the patient""s vasculature through an incision made in the femoral artery in the groin and is used to guide the insertion of other catheters and devices to the desired site. A guidewire is then advanced until its distal end reaches a site proximal to the occlusion. Fluoroscopy is typically used to guide the guidewire and other devices to the desired location within the patient. The devices are frequently marked with radiopaque markings to facilitate visualization of the insertion and positioning of the devices within the patient""s vasculature.
In contrast to previous methods, in one embodiment the guidewire does not cross the occlusion prior to aspiration with an aspiration catheter or other suitable catheter which can provide aspiration pressure. Instead, an aspiration catheter is inserted over the guidewire and the two are concomitantly moved past the occlusion, proximal to distal, while aspirating, to prevent material which dislodges or breaks off the occlusion from entering the vasculature and producing distal emboli.
A guidewire having an occlusive device on its distal end is preferably used in the present method. The method can be effectively carried out, however, using a number of guidewires or catheters that perform the function of occluding the vessel and allowing for the slidable insertion of various other catheters and devices. A standard guidewire can also be used to initially cross the occlusion, and then exchanged with a guidewire having an occlusive device at its distal end. When the standard guidewire is used, it may also be delivered with the aspiration catheter so that both are moved past the occlusion while aspirating. The occlusive device should be capable of preventing the migration of particles and debris from the working area, either through total or partial occlusion of the vessel. The occlusion of the vessel need not be complete.
As the guidewire and aspiration catheter cross the occlusion, blood enters the vessel and keeps any particles dislodged during the procedure from flowing in a distal to proximal direction. In addition, the blood pressure and flow provides the irrigation necessary for aspiration.
After the distal end of the guidewire having an occlusive device is delivered past the site of the occlusion and aspiration is complete, the occlusive device is activated, preventing particles and debris from travelling downstream. Therapy can then be performed to remove or reduce the occlusion. A therapy catheter can be used if desired. The therapy catheter can be any of a number of devices, including a balloon catheter used to perform angioplasty, a catheter which delivers a stent, a catheter for delivering enzymes, chemicals, or drugs to dissolve and treat the occlusion, an atherectomy device, or a laser or ultrasound device used to ablate the occlusion. Alternatively, the therapy catheter can be eliminated and use of the guide catheter or the aspiration catheter alone can be used to aspirate the occlusion. This method is especially useful to remove emboli from the coronary arteries following acute myocardial infarction, because the aspiration catheter can be made small enough to enter the coronary arteries.
Once the desired therapy is performed, the therapy catheter is withdrawn from the patient""s body and the aspiration catheter can once again be delivered over the guidewire if desired to remove any particles or debris created during therapy.
The method described herein provides an improved method for reducing distal embolization during treatment of emboli, thrombi and other types of occlusions in the human arterial or venous system, and is especially useful following myocardial infarction.
Further aspects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiments and the drawings referenced herein, the invention not being limited to any particular embodiment.